Monoamine oxidase (MAO) is primarily responsible for the neuronal degradation of biogenic amines. This enzyme is expressed in all cells; two types of activity (A and B) can be distinguished by their substrate specificity and drug sensitivity. We will study biochemical and genetic properties of this enzyme using cultured cells -- continuous lines of neuroblastoma, hepatoma and L-cells, as well as normal human fibroblasts. The protein composition of this membrane-bound enzyme will be analyzed using gel electrophoresis and autoradiography. (3-H)Pargyline (an irreversible inhibitor) will be used to label the enzyme. Proteins will be separated using isoelectric focusing and non-equilibrium pH gradient electrophoresis under solubilizing conditions. We will determine the number of protein species associated with A and B types of activity and whether differences in electrophoretic mobility exist based on types of activity or species of origin. Selection techniques will be developed to obtain cells varying in expression of MAO activity. Cells with MAO activity will be selected by their ability to survive exposure to drugs whose toxicity is alleviated by deamination, cells without activity by the toxicity of aldehydes formed from MAO substrates. Established techniques of somatic cell hybridization will be used to map the chromosomal location of genes responsible for activity. Phenotypic variants and cell hybrids will be used to assess the number of gene loci involved in expression enzyme activity and the genetic basis of differences between A and B types of activity. We will also look for endogenous polymorphisms of MAO in the normal human population. Skin fibroblasts will be used which express predominantly A type activity. Activity from different individuals will be compared with respect to reaction velocity, substrate affinity, heat sensitivity and electrophoretic mobility. The amount of enzyme protein will be determined by titation against pargyline. These studies will provide insight into the molecular nature of MAO and inherited variations in enzyme activity.